Disclosure about Fair Value of Financial Instruments - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Financial assets:
Equity securities	$ 8,034,000
Restricted cash	89,643,000	$ 100,849,000	[1]
Carrying Amount
Financial assets:
Equity securities	8,034,000	15,685,000
Cash and cash equivalents	303,423,000	284,917,000
Restricted cash	89,643,000	100,849,000
Foreign currency forward contracts, interest rate swaps and cross currency swaps	210,837,000	18,554,000
Financial liabilities:
Borrowings under unsecured credit facility and commercial paper program	844,985,000	1,587,597,000
Senior unsecured notes	10,218,853,000	10,336,513,000
Secured debt	2,901,232,000	2,990,962,000
Foreign currency forward contracts, interest rate swaps and cross currency swaps	87,557,000	53,601,000
Redeemable OP unitholder interests	94,048,000	121,440,000
Carrying Amount | Mortgage loans receivable
Financial assets:
Loans receivable	96,480,000	145,686,000
Carrying Amount | Other real estate loans receivable
Financial assets:
Loans receivable	124,748,000	124,696,000
Carrying Amount | Non-real estate loans receivable
Financial assets:
Loans receivable	373,179,000	336,854,000
Fair Value
Financial assets:
Equity securities	8,034,000	15,685,000
Cash and cash equivalents	303,423,000	284,917,000
Restricted cash	89,643,000	100,849,000
Foreign currency forward contracts, interest rate swaps and cross currency swaps	210,837,000	18,554,000
Financial liabilities:
Borrowings under unsecured credit facility and commercial paper program	844,985,000	1,587,597,000
Senior unsecured notes	10,565,256,000	11,400,571,000
Secured debt	3,032,376,000	3,041,893,000
Foreign currency forward contracts, interest rate swaps and cross currency swaps	87,557,000	53,601,000
Redeemable OP unitholder interests	81,717,000	121,440,000
Fair Value | Mortgage loans receivable
Financial assets:
Loans receivable	96,702,000	150,217,000
Fair Value | Other real estate loans receivable
Financial assets:
Loans receivable	123,101,000	128,512,000
Fair Value | Non-real estate loans receivable
Financial assets:
Loans receivable	$ 418,221,000	$ 379,239,000

[1] The consolidated balance sheet at December 31, 2019 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements.